The invention relates to chemical mechanical polishing of substrates, and more particularly to a polishing pad with a partial adhesive coating, and to methods and apparatus for producing such polishing pads.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes successively more non-planar. If the outer surface is non-planar, then photolithographic techniques to pattern photoresist layers might not be suitable, as a non-planar surface can prevent proper focusing of the photolithography apparatus. Therefore, there is a need to periodically planarize this substrate surface to provide a planar layer surface.
Chemical mechanical polishing is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head, with the surface of the substrate to be polished exposed. The substrate is then placed against a rotating polishing pad. In addition, the carrier head may rotate to provide additional motion between the substrate and polishing surface. Further, a polishing slurry, including an abrasive and at least one chemically-reactive agent, may be spread on the polishing pad to provide an abrasive chemical solution at the interface between the pad and substrate.
A typical polishing pad includes a hard top layer and a softer bottom layer. The top layer has a high friction polishing surface, capable of transporting slurry, and a second surface adhesively bonded to a first surface of the bottom layer. A second surface of the bottom layer is typically attached to a platen by a high strength pressure-sensitive adhesive layer.
One consideration in the production of integrated circuits is process and product stability. To achieve a low defect rate, each substrate should be polished under similar conditions, i.e., same polishing surface structure. A limitation on process stability, as well as polishing throughput, is xe2x80x9cglazingxe2x80x9d of the polishing pad. xe2x80x9cGlazingxe2x80x9d occurs when the polishing pad is frictionally heated and compressed in regions where the substrate is pressed against it, as well as worn as a result of the abrasive contact. The peaks of the polishing pad are pressed and worn down and the pits of the polishing pad are filled up, so the surface of the polishing pad becomes smoother and less abrasive. As a result, the polishing time required to polish a substrate increases. Therefore, the polishing pad surface must be periodically returned to a more uniform abrasive condition, with higher friction and ability to transport slurry. This process is defined as xe2x80x9cconditioningxe2x80x9d and serves the purpose of maintaining a high polishing rate. The conditioning process can be destructive for the polishing pad and results in reducing the lifetime of the polishing pad. Because of these reasons the polishing pad needs to be removed from the platen and replaced every 100 to 1000 substrates, depending upon the type of substrate and conditioning process.
In order to remove the pad, an operator reaches into the polishing area, grasps the polishing pad by hand or with mechanical aids and pulls it to peel it off the platen. Because of the high strength of the adhesive layer, the operator must apply a large force to pull the polishing pad off the platen. For example, the operator may need to apply pulling force of approximately 100 pounds. This large force can exceed the physical abilities of the operator and can pose a risk of injury.
In general, in one aspect, the invention features a polishing pad including a first layer having a polishing surface, and a second layer having an adhesive region and a cured region disposed on a surface of the first layer opposite the polishing surface.
Implementations of the invention may include one or more of the following features. The polishing pad may have a plurality of adhesive and cured regions. The cured regions may be partially or entirely cured. The cured regions may be circles or arc segments arranged in a pattern. The cured region and the adhesive region may form concentric circles. A third layer may be disposed between the first and second layers opposite the polishing surface.
In general, in another aspect, the invention features an apparatus for selectively altering a polishing pad adhesive layer. The apparatus includes a radiation source generating a radiation beam, a support for the polishing pad, and a mask having a transparent region and an opaque region. The mask is disposed between the radiation source and the substrate holder, such that the radiation passes through the transparent region and is blocked by the opaque region. A shutter may be disposed between the radiation source and the mask.
In general, in another aspect, the present invention features a method for selectively altering a polishing pad adhesive layer. The method includes: providing a mask having a transparent region and an opaque region and directing radiation toward the mask so that the radiation is blocked by the opaque region and passes through the transparent region to impinge on the adhesive layer on the polishing pad, whereby the area of the adhesive layer corresponding to the transparent region of the mask is cured to be less adhesive.
Implementations of the invention may include one or more of the following features. The radiation may be ultraviolet light. The transparent region may be made of ultraviolet light transparent quartz or polymer material. The mask may be made of ultraviolet light blocking material such as paper metal, ceramic or polymer material. The transparent region may be an opening in the mask. The transparent region and the opaque region may form concentric circles. The mask may have a plurality of transparent and opaque regions. The transparent regions may be circles or arc segments arranged in a pattern. The ratio of the cured region surface to the adhesive region surface may be between about 10 to 30%. The polishing pad may be exposed to the radiation for a time varying between about 5 to 60 seconds. The radiation intensity may vary between about 100 to 1200 Watts/inch.
In general, in another aspect, the invention features a method for selectively altering a polishing pad adhesive layer. The method includes: providing a polishing pad having a layer of adhesive that covers substantially an entire surface of the pad, and curing selected portions of the adhesive layer to reduce adhesive strength of the layer.
Among the advantages of the invention may be one or more of the following. By selectively altering a polishing pad adhesive layer the strength of the adhesive layer is reduced. This reduces the force applied to remove the polishing pad off the platen and the risk of injury for an operator.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments, and from the claims.